Plumbing in Un-Heated Structure

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TVJoe

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May 19, 2019
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NY
Hello,

I am working on an out building. One of the things we were looking to do is to place a bathroom (Toilet/Sink), in the structure. This structure will not be heated at all during the winter. I will blow out the water line going to it.

I hired an architect to draw up the building. He did a good job with the overall design but one thing has me concerned.

The foundation perimeter will be dug down 42in (trench footer). This is what the structure will be sitting on and is below the frost line. Then we will have a thermal break around the footer and under the slab. Then the slab will be poured inside the footer.

I get that the structure (walls) will not be going anywhere since its below the frost line. But what about slab? If I have plumbing coming up from the slab will I ever get any heaving since the slab is not below the frost line. The slab will only be 4in thick with i think 4in of stone under it.

I am worried about the plumbing come in and if the slab goes up or goes down from frost heave. Would it not destroy the plumbing?

Any other tips so I can make sure the plumbing is done correctly?

Drawing is attached of how the foundation will be done.

Thanks!
 

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They make insulated pex service line. The trick is to make sure everything drains back to a common drain.
 
I think a little more detail on the exact thinking/logic would be very helpful to the OP.

Not quite sure how the insulated service line serves a purpose, since it would below the frost level.
 
Yes more detail please. Also how about for the sink and toilet sewer line? I am worried about both breaking if the slab moves. Or maybe the slab wont move?
 
Embed the lines in sand several feet below the slab, wrap the penetrations in about half an inch of foam, to protect them in case the slab moves, and do a good job of compacting a good base and the slab should not move.

Have a shut off just outside the building for the water feed, and a tee between it and the building with a drain valve, which runs to a vertical drain pipe, typically I install 4-inch diameter pvc pipe and cap, with a foot or two drop below where the the line runs into it, to act as a pump out well. For the valves use Minneapolis patterns with the attached riser, and stem. Install a tee after the shutoff valve to the water heater with a pressure gauge, another ball valve, and an air chuck after the valve so you can pressurize the system.

For winter:
You read the pressure gauge to see what the pressure is;
Shut off the feed to the building, and connect the air chuck to the one on the system with the compressor regulator set to just under the system pressure.
Turn off the water heater, and then use the compressor to pressurize the building;
Open the hot taps one at a time and drain out the hot water;
After you drain all the hot water, do the cold water, leave the sill cock closed for the toilet, until you drain the rest of the cold, and do it last;
Then go back and blow out the hot until there isn’t an more vapor coming out and you have dry air. Do the same with the cold side.
Take the cap off the drain riser, and then open the valve to the drain tee until you get good air flow. Look out it will purge water into the air. When the bubbling subsides, close the drain valve.

Put a quart of RV antifreeze, into each drain. For the toilet, add it through the overflow tube, so that it gets into all the passages.

The building is now winterized.
 
Thank you for the detailed reply. What type of pipe should be used for this? I would imagine there will need to be some pipe work done under the slab. Connecting the drains for the toilet and sink plus connecting in the vent pipe. I would think that all needs to be done in the gravel under the slab?
 
I cut my teeth, in Vegas, where everything, that isn’t a higher end custom, is built as slab on grade. You run a PEX run for the main water feed, and then wrap it in the foam they sell as sill seal, and run it up through the slab. The sewer is just standard ABS.

We winterize about a hundred buildings every fall, and open them back up in the spring. The water heater tank acts as an oversized pressure tank, for the air, and gives you enough air volume to generate enough velocity in the water ines to move any droplets on out of the end.

I did forget one step, which is to remove the aerators, and the shower head. They have built in restriction to limit the flow, and you want as much flow as possible to flush out the water.

If I had CAD software at home I’d draw you some pictures.
 
Heat energy always wants to move from hot to cold. What a lot of people don't seem to get is that insulation does not stop the transfer of heat, it only slows it down. Wrapping anything in insulation that does not have a source of heat will eventually be at the same temperature on both sides of the insulation. [If no water runs through the PEX insulated pipe in a space subject to freezing, the PEX will eventually freeze].
The second thing to pay attention to is location. The OP listing shows New York. The climate there is quite different from Las Vegas.
The ground freezes and expands to create frost "heave" only when the ground is cold enough and only if there is a lot of moisture in the soil. If the soil is well drained (such as with sandy soils) there is not much chance of heaving. If the soil is not well drained (such as with clay soils) there will be heaving. IF there is enough insulation between the foundation and the earth, the heat of the earth will keep the ground from freezing. The 2 inches of XPS rigid insulation in your drawing is not enough and does not extend far enough out to keep the ground from freezing and heaving.
The "Floating" slab has been used very successfully in Scandinavia for several decades. There is no frost wall below the frost line, and a monolithic slab is poured over several inches of rigid insulation, which also extends 4-6 ft. out from the slab.
Here is the IRC code section on that: International Residential Code section R403.1.4.1 Frost protection
 
Fixitron,

Are you saying this is not a good design and I will have issues? My soil is a ton of rock. I cant dig more than 3 inches without hitting one. I never have puddles in my yard so I would say it drains very well. Would the footer not act as a frost wall? Its is going to be 42in deep. That is below my frost line and goes all the way around the structure.

Thanks!
 
Yes, that is what I am saying. Your plan calls for 2" of XPS, for an R-10. In New York in the winter, it gets very cold. When temps get in the single digits, the ground beneath could freeze, heaving the slab. In addition, the insulation is only shown under the slab and not under or around the perimeter or frost walls.
Not seeing puddles in your yard is not an indicator of well drained soil. Water could still be below the surface.
Read up on "frost protected shallow foundations".
 
So the outer footer you don't think would act as a frost wall?
 
A frost wall is designed to keep the foundation wall from moving due to heaving when the wet ground freezes and expands. Normally, the heat of the house will keep the slab from heaving. With no heat in the house and only R-10 under the slab, the heat from the earth may not be able to keep the ground under the slab from freezing when the temperature in the house gets very cold. If the insulation stops at the slab, the ground under the slab's perimeter can freeze.
I have seen it in Vermont with garages. It all depends on the soils and temperatures.
 
Hello,

I am working on an out building. One of the things we were looking to do is to place a bathroom (Toilet/Sink), in the structure. This structure will not be heated at all during the winter. I will blow out the water line going to it.

I hired an architect to draw up the building. He did a good job with the overall design but one thing has me concerned.

The foundation perimeter will be dug down 42in (trench footer). This is what the structure will be sitting on and is below the frost line. Then we will have a thermal break around the footer and under the slab. Then the slab will be poured inside the footer.

I get that the structure (walls) will not be going anywhere since its below the frost line. But what about slab? If I have plumbing coming up from the slab will I ever get any heaving since the slab is not below the frost line. The slab will only be 4in thick with i think 4in of stone under it.

I am worried about the plumbing come in and if the slab goes up or goes down from frost heave. Would it not destroy the plumbing?

Any other tips so I can make sure the plumbing is done correctly?

Drawing is attached of how the foundation will be done.

Thanks!


Joe,
I read your question but did not read all the comments. So excuse if this has already bee addressed
Insulation,
Insulate the water lines with 1'' rubbertex insulation. I would suggest that you insulate the whole line under the slab, The insulation will stop rocks and pebbles from rubbing on the pipe, and the slab can move
the sewer lines, wrap them where they come through the slab with insulation also

insulation.png
 
Plumbing in the unheated area needs proper care and supply of heat so that the pipes should not get frozen in the exterem cold. You can do adequate insulation around the pipes and make sure that they have some contact with heat..
 

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